Linear block copolymers of polystyrene and polydimethylsiloxane have been synthesized, both by graft and block copolymerization. In block copolymerization of such linear polymers, polystyrene is produced by anionic polymerization with an organo lithium initiator and the living polymer (PS.sup.- Li.sup.+) created thereby is reacted with hexamethylcyclotrisiloxane, (Me.sub.2 SiO).sub.3, in the presence of a polar promoter wherein a block of polydimethylsiloxane (PDMS) grows on the end of the living polystyrene block. These polymers are useful for impact modification of engineering thermoplastics and forming coatings with low energy surfaces. PDMS exhibits superior heat resistance, low-temperature flexibility, weather resistance, chemical inertness.
U.S. Pat. No. 5,618,903 describes an anionically polymerized polyethylene(PE)-PDMS block copolymer with increased molecular weight, strength, service temperature stability and purity. The PE blocks exhibit the high level of crystallinity and high melting point of high density polyethylene and thus give higher strength and service temperature capability to the block copolymers.
U.S. Pat. No. 5,300,609 describes a fluorosilicone block copolymer useful in silicone/fluorosilicone rubber mixtures. These fluorinated siloxane polymers have two major advantages over a non-fluorinated siloxane. One is their lower surface tension property and the other is their more chemical resistant nature. In Makromol. Chem., 194(5), 1403-10, Kobayashi describes a polydimethylsiloxane-poly(methyl-3,3,3-trifluoropropyl-siloxane) copolymer blend having improved fuel and oil resistance over PDMS polymers. These fluorosilicone elastomers are prepared as both random and block copolymers using anionic living polymerization techniques. They do not, however, have a polyolefin block that exhibits the high level of crystallinity and high melting point of high density polyethylene necessary to give the polymer higher strength and service temperature capability.
Thus it can be seen that it would be advantageous to be able to produce a block copolymer with the characteristics of the PE-PDMS described in the '903 patent in addition to heat, weather and chemical resistance, and low temperature flexibility. PE-PDMS copolymers when coextruded with polyethylene and other polyolefins quickly migrate to the surface, leaving in effect, a surface coated with the low-surface energy PDMS block. However, in some cases PE-PDMS polymers are not sufficiently efficient in migration rates to the surface in the time frame of residence time in the extruder. This leads to unacceptable utilization levels of these high value materials. The present invention describes a copolymer that meets these needs and is highly useful in release coatings. The fluoro-containing PE-PDMS polymers of this invention impart both a stronger driving force to the surface and faster migration (more efficient use).